Working principle

Optical fog detectorONED250Using backscatter technology to measure the number of water droplets in fog that affect visibility in the atmosphere. The detector emits a narrow infrared beam through an opening at the front end. A prism is embedded in another opening, and there is a sensor behind the prism to receive the backscattered laser signal with a narrow field of view. This sensor is used for receiving/The laser within the narrow overlapping area of the luminous beam is very sensitive. After receiving the light signal, the sensor will output a raw signal. The sensitive area is approximately located at the front end of the sensor30 cmAt this location, its volume is approximately1 cm³.

Electronic signal

The original signal is an analog signal, which is the number of backscattered light rays from the overlapping area. So the bigger the fog, the more signals are transmitted back.

Signal Processing

visibilityVISIt can be exported as follows:

VIS = Konst/ V

VIS: Visibility (unit)m）；

VThe original signal level measured;

KonstFor the calibration constant.

If the measurement signal is too low, below noise and temperature drift, it is determined that there is no fog. From this, the upper limit of measurable visibility can be set (set as5000Rice). In order to obtain similar visual visibility values, samples are generally taken1Minutes, take the average as the measurement result. Everything described here is done through a microprocessor: first, a one minute sample is averaged, and then the visibility of the fog is obtained based on the following graph.

Result output

Digital signal output

The calculated visibility value isASCIIThe form of the code string isRS232Port display（2400 baud 8N1）And transmit it every minute. The reading method can also be (optional). A typical visibility number string is as follows:

"+0.00000,10000,05200,00005 "The four numbers represent extinction, visibility (in meters), laser power, uncalibrated ambient light visibility, fog density, and extinction in sequence. The relationship between extinction and fog density is as follows: visibility= 3/extinction

These data strings can be accompanied byRS232The data logger of the port can receive it, or it can be installed with terminal software (such asHyper TerminalofPCreceive. We recommend free softwareBr@y.

The microprocessor also controls a potential free semiconductor switch. When the calculated visibility is lower than the set value (default is1000If the semiconductor switch is turned on, the meter will be turned on. When the visibility exceeds the set value, the semiconductor is turned off.

Analog signal output controlled by microprocessor

The microprocessor also controls the output of analog signals directly providing visibility（VIS=1kmThe result is1VWhenVIS=500mWhen, the result is0.5VAnd so on,5VCorresponding to saturation state5000Rice). This output is updated every minute. When the user switches to analog signal output for the first minute, the instrument displays a value of0.

Position - detector orientation

The installation orientation of the detector should be such that the red light beam faces north and is kept as horizontal as possible, so that sunlight cannot reach the sensor. During the propagation of infrared beams10There should be no direct obstacles within a meter range. The front end of the detector is equipped with a length not exceeding10A centimeter sized protective cap helps to protect against the effects of precipitation (usually the original small cover is already sufficient).

Technical Parameter

Connecting the power supply

voltage------------------------------------------------------------------------------------------------V 12AC（11…15

）electric current 200

-------------------------------------------------------------------------------------------------mAExcluding heating -----------------------------------------------------------------------mA60

about

infraredwavelength 650

-------------------------------------------------------------------------------------------------nmOutput power supply -------------------------------------------------------------------------------------------mW5

less thanLaser safety level -------------------------------------------------------------------------------------

3RWarm-up time 1

-------------------------------------------------------------------------------------------MINInstallation required area (in front of the infrared beam) 10

--------------------------------------------------------------m

boxsize --------------------------------------------------------------------------------------------mm

120*120*90weight 1

--------------------------------------------------------------------------------------------Kgprotection grade -------------------------------------------------------------------------------------

IP65Visibility range -----------------------------------------------------------------------------------m

20..10000

signal output ---------------------------------------------------------------------------------------------V0..5，

analog

---------------------------------------------------------------------------------------------RS2322400 baud 8N1operation temperature